First, I am by no means an expert, but I did pick up on a couple of things you mentioned, so I am posting.
Second, I agree with the other posters here...it is 110% your decision. I 110% support whatever you decide to do.
hugapitbull wrote:With the other minor incidences he was verbally corrected and he acknowledged his response was not acceptable and was apologetic for his actions.
I think you may again be putting human emotions on the dog. From my limited understanding, Duke is probably reacting to the verbal correction, but may not be connecting it to what he did. Not to say I have never yelled at my dog...
I've seen many dogs look sheepish after a correction. Dogs that have torn apart the couch in the morning will look sheepish when their owner gets mad...but they are reacting to the human being mad, not apologizing for (or even recognizing) the action that they took earlier. It sounds as if yours is a more immediate correction, but the same theory applies.
I also see in a later post that you again mention corrections. Some may disagree, but I don't know that this is the route you want to take. Being corrected for giving warnings could lead to him stopping the warnings (not good). I think Duke sounds like a good candidate for clicker training. (A lot of this comes directly from people on this board...thanks to those of you who have given me this advice before!)
I know that you are having difficulty finding good trainers. Have you gotten any books?
http://www.clickingwithcanines.com/id6.htmllists a lot of good resources. I have read
Click to Calm, and have found it very helpful. Haven't read
Bringing Light to Shadow, but it is on my list.
I wish you all the best! It sounds like Duke is in very caring hands. I'm sure you will figure out what is best for all involved.